function y = curly20(x)
%CURLY20 Function
%x0=[0.001/(n+1),...,0.001/(n+1)]
%fmin=f81([0,0,...,0])=0.00125
%Author:cai li
n=length(x);
k=20;
y=0;
for i=1:n
    q=0;
    if i<=n-k
        for j=i:i+k
            q=q+x(j);
        end
    else
        for j=i:n
            q=q+x(j);
        end
    end
    y=y+q^4-20*q^2-0.1*q;
end